1. Field of the Invention
This invention relates to a stent adapted to be inserted into a tubular organ of the human body such as a blood vessel or a ureter to thereby maintain the lumen of the tubular organ open.
2. Related Background Art
For example, in case of the remedy of myocardial infarction or the like, it is practiced to insert an expanding tool called a stent into the strictured portion of a blood vessel, and prevent the obstruction of the blood vessel. Also, in case of the remedy of a ureteric calculus or the like, a stent is sometimes used to maintain the ureter expanded to make the calculus easy to be discharged.
Generally, the stent in its shape of reduced diameter is mounted on the outer periphery of the tip end portion of a balloon catheter and is inserted into a blockaded affected part through a guide catheter, whereafter the baloon of the balloon catheter is inflated and is forcibly widened, and in that state, it is detained in the blockaded affected part to thereby expand the tubular organ.
As an example of the stent of the prior art, Japanese Laid-Open Patent Application No. 6-181993 discloses a stent comprising a plurality of cylindrical elements in dependently expandable in the radial direction thereof and connected together so as to be substantially aligned in a common axis, said plurality of cylindrical elements being connected together with flexibility in the lengthwise direction thereof. Also, as an example of it, there is disclosed a stent comprising a plurality of cylinder elements circumferentially extending in a waveform and annularly connected together, said plurality of cylinder elements being axially arranged at predetermined intervals, portions of these cylinder elements being connected together by an axially extending mutual connecting element.
The stent of Japanese Laid-Open Patent Application No. 6-181993, however, is of such structure that the interval between respective line portions becomes wider uniformly when the cylinder elements forming a waveform are expanded. In such structure, the inner wall surface of a soft tubular organ such as a blood vessel could not be satisfactorily supported by the cylinder elements roughly arranged because the cylinder elements would be got into the inner wall of the tubular organ, and this has led to the undesirable possibility that after the detention, the inside skin increases from this gap, thus causing stricture again.
Japanese Patent Publication No. 6-44910 discloses a stent molded into the form of a snake including a series of straight portions and a plurality of bent portions, said straight portions being coupled together by said bent portions and forming a series of staggered loops, said form of a snake being molded into a cylindrical shape having a longitudinal axis, said straight portions comprising a plastically deformable wire surrounding said axis and bent into a substantially cylindrical form perpendicular to said axis.
However, in the stent disclosed in Japanese Patent Publication No. 6-44910, the straight portions are simply bent into a C-shape as viewed from the end surface thereof and therefore, in addition to the problems raised in Japanese Laid-Open Patent Application No. 6-181993, the holding force after expansion is weak, and this has led to the undesirable possibility that the diameter thereof is reduced by the pressure of the inner wall of a blood vessel, thus causing reconstriction.